Developments in router technology have led to system designs that provide a general-purpose connection-oriented transfer mode for a wide range of services. These services include the simultaneous transfer of integrated traffic (data, voice, and video traffic) over the same network system. To efficiently transmit the integrated traffic, prior art systems have relied on a transmission card that processes multiple channels of voice, video, and data using banks of digital signal processors (“DSPs”). Typically, the transmission card comprises a group of framers coupled to a bank of transmission lines. The transmission card also comprises a time slot interchanger (“TSI”) coupled between the framers and the banks of DSPs.
The TSI is typically a non-blocking switch that can connect any time slot of an incoming time division multiplexed (“TDM”) stream to a different time slot of an outgoing TDM stream. Thus, in the prior art, a bank of transmission lines are multiplexed by the group of framers to generate a TDM stream that is transferred to a first interface of the TSI. Similarly, a bank of DSPs are coupled to a second interface of the TSI. As previously described, the TSI may switch a time slot from the incoming TDM stream to a different time slot of the outgoing TDM stream. Thus, the TSI may transfer data from any one of the transmission lines to any one of the DSPs.
Typically, the DSP that receives the transferred data compresses or otherwise processes the transferred data prior to transmission across a network system. Alternatively, compressed data received by the DSPs may also be uncompressed or otherwise processed and subsequently transferred to one of the transmission lines via the TSI.
FIG. 1 illustrates a prior art transmission system. In particular, system 100 includes a private branch exchange (“PBX”) 110 coupled to a network (150) via card 160. PBX 110 is coupled to card 160 via line 115. Typically, line 115 comprises a transmission line that uses a T1 protocol to multiplex twenty-four digitized voice or data channels onto a single line. Thus, PBX 110 may be coupled to twenty-four different devices.
System 100 uses card 160 to transfer data from a device coupled to PBX 110 onto network 150. For example, in system 100, PBX 110 digitizes data from phone 105 or facsimile 106 and multiplexes the digitized signal onto line 115. Subsequently, framer 120 removes the T1 protocol information from the digitized data and generates a TDM stream that is transferred to TSI 130 on line 116. Similarly, the remaining framers of card 160 (Framer 121–12N) transfer TDM streams from other T1 lines (not shown) to TSI 130 on different lines or in a shared fashion—for example along a wired OR line. TSI 130, in turn, generates an outgoing TDM that is transferred to DSP 140, DSP 141, or DSP 142. Thus, TSI 130 may transfer a time slot of data from line 115 to DSP 140, DSP 141, or DSP 142.
System 100 provides a basic system for connecting PBX devices to a network. Specifically, controller 170 maintains a call connection between the devices coupled to PBX 110 and remote devices coupled to network 150. Typically, controller 170 sets up or tears down the call connections between the devices coupled to PBX 110 and remote devices coupled to network 150 using a switch virtual call protocol or a permanent virtual call protocol. Accordingly, in response to a call set up message, controller 170 instructs TSI 130 to switch time slots from line 115 to a DSP of card 160, thus transferring data between network 150 and a device coupled to PBX 110.
For example, in response to a call set up message, controller 170 may transfer a voice call from phone 105 to a remote device coupled to network 150. Alternatively, controller 170 may transfer data from facsimile 106 to a remote device coupled to network 150, thus resulting in a flexible call connection system. Although system 100 provides a flexible call connection system, the complex interconnectivity of system 100 results in numerous disadvantages during the transmission of voice calls. In particular, voice calls require a reliable system to ensure a high quality of service between different customers. One disadvantage results from an interconnectivity error reducing the voice transmission reliability of system 100. Another disadvantage results from a DSP error reducing the voice transmission reliability of system 100.